Want to design PIFA w/ U-shaped Slots for Cellular Communication - Beginner, help!

Hi I'm a beginner using CST and I was wondering if anyone could help me to design a PIFA with U-shaped slots. I've taken an antennas course so I'm familiar with most of the terminology, but am not familiar with CST. I am able to create a PIFA fairly easily using an antenna design tool, but the U-shaped slot I am having trouble with. It looks like like the attached photo.